The present invention relates to a system and method for managing slurry used to cut workpieces in cutting machines, such as wire saws or the like. More particularly, the present invention pertains to a slurry managing system and a slurry managing method that optimally control the properties of the slurry supplied to the cutting machines.
A wire saw is typically employed to cut workpieces, such as silicon ingots, or the like, into wafers. The wire saw includes a plurality of rollers and a single strand of wire, which is spirally wound about the rollers with a predetermined pitch between each winding. The wire is guided by the rotation of the rollers. During rotation of the rollers, slurry containing abrasive grains is fed to the wire. In this state, a workpiece is pressed against the wire to cut the workpiece into a plurality of wafers simultaneously.
The slurry is an aqueous or oleaginous liquid (dispersing liquid) in which abrasive grains are dispersed. The wire saw is provided with a managing system to prepare and manage the slurry. The managing system includes a preparing tank, in which abrasive grains and dispersion liquid are mixed to prepare the slurry. The slurry prepared in the preparing tank is fed to the wire saw.
It is preferred that the used slurry, which has been used by the wire saw to cut workpieces, be recycled to reduce the costs of cutting the workpieces. However, used slurry includes impurities, which are fine grain components that are smaller than the abrasive grains. More specifically, the used slurry includes impurities such as cutting chips of workpieces and fragmented abrasive grains. The impurities decrease the cutting capability of the wire saw.
The management system includes a separating apparatus that separates the impurities from the used slurry and recovers the recyclable abrasive grains and dispersing liquid. The recovered abrasive grains and dispersing liquid are returned to the preparing tank to be mixed with additionally supplied fresh abrasive grains and dispersing liquid to be prepared as slurry again. The slurry is then fed to the wire saw from the preparation tank and thus recycled.
The cutting performance of the wire saw depends greatly on the nature of the slurry fed to the wire, for example, the mixed weight ratio of the abrasive grains and the dispersing liquid. Thus, the properties of the slurry in the preparing tank must be maintained at optimal values to maximize the cutting performance of the wire saw. However, if the abrasive grains and dispersing liquid recovered by the separating apparatus are returned to the preparing tank, the properties of the slurry in the preparing tank fluctuates in accordance with the amount of the returned abrasive grains and dispersion liquid. This may hinder cutting.
Furthermore, fluctuations in the temperature of the used slurry or in the amount of impurities included in the used slurry change the properties (e.g., specific gravity or viscosity) of the used slurry. The changes in the properties of the used slurry alter the separating efficiency of the separating apparatus. This may hinder recovery of the abrasive grains and dispersing liquid from the used slurry or leave impurities in the recovered abrasive grains and dispersing liquid.